From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from snark.thyrsus.com (static-71-162-243-5.phlapa.fios.verizon.net [71.162.243.5]) by huchra.bufferbloat.net (Postfix) with ESMTP id BAC3B2004D7 for ; Wed, 14 Mar 2012 11:43:18 -0700 (PDT) Received: by snark.thyrsus.com (Postfix, from userid 1000) id E221E40617; Wed, 14 Mar 2012 14:42:58 -0400 (EDT) Date: Wed, 14 Mar 2012 14:42:58 -0400 From: "Eric S. Raymond" To: Patrick Maupin Message-ID: <20120314184258.GA30210@thyrsus.com> References: <20120314104920.697EA40617@snark.thyrsus.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Organization: Eric Conspiracy Secret Labs X-Eric-Conspiracy: There is no conspiracy User-Agent: Mutt/1.5.21 (2010-09-15) Cc: thumbgps-devel@lists.bufferbloat.net Subject: Re: [Thumbgps-devel] USB handshake signals and Linux X-BeenThere: thumbgps-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list Reply-To: esr@thyrsus.com List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 14 Mar 2012 18:43:18 -0000 Patrick Maupin : > The FTDI devices have a latency timer that allows you to control this > somewhat. I found a couple of hits on the search "PL2303 latency timer" that implies it has one too. But I doubt the value of the latency timer will be relevant for handshake-line notifications; see below. > But even better, if we're going to use the PPS signal, they > essentially guarantee that they will send ASAP on modem control signal > change. We might need to characterize "ASAP" but I would hope that it > doesn't vary too much. Probably not. Trying to buffer a handshake state change doesn't make any sense. I'm not surprised that the FTDI gives them realtime priority and I *will* be surprised if the PL2303 (or any other adapter) doesn't do likewise. -- Eric S. Raymond